This invention relates to a device, including a fan and a fan shroud, for introducing cooling air through a heat exchanger and discharging the cooling air so as to increase the cooling effects of the cooling air when the heat exchanger is located in front of an engine in an automotive vehicle.
Recently, it has become important in automotive vehicles to make the engine room or compartment smaller in order to allow the passenger compartment to be made as large as possible without increasing the overall size of the vehicle. Further, various kinds of accessories, such as a condenser and a compressor for an air conditioner, a compressor for a power steering, an ABS (Anti-lock Brake System) and so on, are located in the engine room. Thus, a space occupied by the fan, the engine behind the fan, and the accessories must be made as small as possible. A fan must be provided for cooling the condenser and the radiator. Airflow is created by rotation of the fan, and the heat of the radiator and the condenser is radiated into the airflow. Generally, air introduced from a front end of the vehicle flows through the condenser and the radiator and is discharged from the back of the fan into the engine compartment.
For improving a cooling effect of the fan, a shroud is provided between the cooled devices and the fan, so that the air utilized for heat exchange from e.g. the condensor and radiator is guided by the shroud and discharged directly to the engine and other devices. A "covering rate" of the shroud represents the axial proportion of the fan covered by the downstream end of the shroud. As shown in FIG. 20, the covering rate K is defined by the function K=Y/X.times.100. FIGS. 21A and 21B respectively show a fan with a high covering rate and a fan with a low covering rate. As shown in FIGS. 21A and 21B, in the fan with the high covering rate, air turbulence is small adjacent the outer periphery of the fan, because the fan is covered with the shroud so that wraparound of air from a positive pressure surface to a negative pressure surface is small. Air discharged from the fan is prevented by the shroud from spreading in the radial direction, so that the air tends to be discharged straight backward. However, when the covering rate is from 60% to 70% or less as shown in FIG. 21B, the discharged air is not influenced by the distance between the fan and the engine etc., as shown by a chain line (alternate long and two short dashes) in FIG. 19. This is because discharged air of the fan spreads in the radial direction of the fan (See FIG. 21B).
However, when the covering rate is high (80% or more), as shown in FIG. 21A, air turbulence becomes small in the outer periphery portion of the fan, so that advantages such as decreased noise, improved cooling effect of the fan and so on are achieved. However, as shown in FIG. 19, the influence of the distance between the fan and the engine structure or the like becomes large (solid line in FIG. 19). This is because it is difficult for the discharged air to spread in the radial direction as compared with the case in which the covering rate is low, and the air strongly tends to be discharged straight backward (see FIG. 21A). Thus, the discharged air collides with the structures such as the engine or the like (i.e. obstacles) so that the cooling effect of the discharged air is reduced thereby requiring the fan to be driven with greater frequency and resulting in greater energy usage. In particular, as a result of research into the performance of various kinds of the fans, it was recognized that the quantity of the airflow decreased considerably as shown by the solid line in FIG. 19 when the distance between the fan and the obstacles, especially the engine, is less than about 200 mm.
A fan, in which outer peripheral portions of the blades are connected by a cylindrical ring, that is, a ring fan, has two kinds of covering rates. First, a ring covering rate K2 indicates the axial proportion of the blade covered by the ring, as shown in FIG. 23, and this ring covering rate K2 is represented by the function K2=Y/X.times.100.
Second, a shroud covering rate K1 indicates the axial proportion of the fan covered by the shroud. This shroud covering rate K1 is represented by the function K1=Y/X.times.100, as shown in FIG. 22. These covering rates K1 and K2 for the ring fan have the same effects and problems as discussed above for the shroud covering rate.
In a prior art PCT Patent Publication S61-502267, a fixed member is located behind a fan. The fixed member has a control surface for removing the airflow component in a rotation direction to allow the air to discharge straight along the axial direction of the fan. However, it is clear that, in this prior art arrangement, discharged air is directly influenced by the distance between the fan and obstacles, such as an engine, such that it will experience a decrease of the quantity of discharged air when the obstacles are near the fan.